Apparatus for producing porous metal plates



May 22, 1956 M. A. COMLEY 2,746,742

APPARATUS FOR PRODUCING POROUS METAL PLATES Filed Aug. 27, 1952 2 SheetsSheet 1 A ttnrney May 22, 1956 M. A. COMLEY 2,746,742

APPARATUS FOR PRODUCING POROUS METAL PLATES Filed Aug. 27, 1952 2 Sheets-Sheet 2 In ve n (or MF/W/m i/rffla/fmzzy I A Home y United States Patent APPARATUS FOR PRODUCING POROUS METAL PLATES Mervyn Arthur Comley, Solihull, England, assignor to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware Original application March 24, 1949, Serial No. 83,164. Divided and this application August 27, 1952, Serial No. 306,588

Claims priority, application Great Britain March25, 1948 6 Claims. (Cl. 266-6) The present invention relates to the production of porous metal plates and, more particularly, to an apparatus for the production of porous metal plates of high porosity.

Porous metal plates of high porosity may be produced by sintering metal powders in a reducing atmosphere. In order to obtain high porosity, that is to say, to make the voids constitute at least 55% and even from 80 to 90% of the volume, it is usual to form the plates with the aid of a spacing agent which volatilizes during the sintering operation. This procedure however has the disadvantage that the size and shape of the pores in the sintered metal are affected by the size and shape of the particles of spacing agent, which are difiicult to control. Further, if the gases that are evolved are allowed to escape freely during the sintering the plate may be distorted and if the gas is allowed to escape only through restricted openings the powder may be displaced before it sinters. The need for a spacing agent can be obviated by employing metal powders of low bulk density which are characterized in bulk by a large number of voids. These powders are typified by nickel powder prepared by decomposing nickel carbonyl. The nature of the powder and its bulk density depend upon the conditions under which the carbonyl is decomposed; and the powders can, for example, be of two different kinds, which may respectively be A-nickel and B-nickel. A-nickel powder consists essentially of particles which may vary in size from 2 to microns and which form compacts in which the particles are mechanically but very loosely held together. The bulk density of A-nickel powder varies from 0.6 to 4.5 grams per cubic centimeter. B-nickel powder consists essentially of smaller particles than Anickel, but these particles are interlocked into aggregates which are not only stronger than the loose compacts of A-nickel but also are themselves interlocked. Accordingly, the bulk density of B-nickel powder is lower and varies from about 0.3 to about 1.2- grams per cubic centimeter. The lower the bulk density, the higher the porosity of the final sintered product, but at the same time the higher is the contraction during sintering.

Because of the different natures of A-nickel and B-nickel the porosities of plates made from them differ. High porosities can be obtained with B-nickel despite the contraction during sintering. A-nickel, on the other hand, tends to crack during sintering and if it is first compressed to an extent suiiicient to eliminate cracking the porosity is reduced to a comparatively low figure, which may be no more than 50%.

The contraction which takes place during sintering leads to distortion, but undistorted plates of uniform size, thickness and shape can be produced if the direction of the contraction is controlled. Control may be effected by confining the contraction substantially to one direction in such a way that the mass of powder is reduced in thickness during sintering, but not in length or breadth,

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For this purpose, a wire-mesh grid may be incorporated, but a grid cannot be introduced into a thin plate without great difficulty. Even if a thin plate is made with a grid in it, the grid causes loss of porosity and increases the weight.

It is an object of the present invention to provide apparatus for producing porous metal plates of high porosity without distortion and of uniform size, thickness and shape.

It is another object of the invention to provide apparatus for producing highly porous sintered metal plates without any substantial contraction in the direction parallel to the major faces of the plates.

Among the further objects of the present invention is to provide means or apparatus adapted to produce sintered metal plates having high porosity wherein the voids constitute at least 55% and preferably from to of the volume.

It is also a purpose of the invention to provide apparatus operative to produce sintered metal plates up to about 4 millimeters in thickness and of a porosity wherein the voids constitute from 80% to 90% of the volume, such plates being capable of use with particular advantage as accumulator plates or battery electrodes.

Another object of the invention is to provide an improved apparatus for making sintered porous metal plates of high porosity having voids constituting at least 55% of the volume of the plates and for conducting the sintering operation in a manner to restrain contraction parallel to the major axes of the plate and under conditions which permit easy separation of the plates from the mold surfaces and which avoid contamination of the mold surfaces by traces of the partially sintered metal.

Other objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 illustrates a diagrammatic elevation of an apparatus embodying the features of the invention;

Fig. 2 depicts a vertical section through some of the molds forming part of the apparatus shown in Fig. l, and

Fig. 3 is a cross section taken on line 3-3 of Fig. 2.

Broadly stated, this invention contemplates the provision of an apparatus for forming a plate between two formers having roughened or corrugated surfaces, the depth or" the surface roughening or corrugations being very small but serving to prevent contraction parallel to the main surfaces of the plate. The formers may consist of carbon, with corrugations made by cutting fine grooves in the surface. The shape of these corrugations is imparted to the sintered plate and the carbon formers tend to burn away during use. The formers may also be made from a nickel-chromium alloy similarly corrugated, but there is a small tendency for the sintered plates to become united to the alloy by the sintering.

Formers made from unglazed ceramic materials are preferred. Of course, the ceramic material must be resistant to the temperatures attained during the sintering. Either fused alumina or sillimanite is a suitable material and it has been found that, if it has a matte surface, it need not be corrugated or otherwise further roughened in order to prevent contraction of the sintered material across the face of the former.

If high porosity is to be obtained, B-nickel powder or iron or other powder of similar physical shape and density to B-nickel powder should be used.

In carrying out the invention, a forming plate made from a ceramic material with a rough surface may, for instance, cover the bottom of a shallow mold of a nickelchromium alloy. Metal powder in excess of that required to fill the mold is removed by a knife edge and a second forming plate similar to the first is placed on the powder. The assembly is then passed through a sintering furnace. During the sintering process the pressure on B-niekel or similar powder should be from lb. to 10 lbs. per square foot of plate surface, although considerably higher pressures may be applied before sintering in order to control the porosity of the finished plate.

In order to distribute the powder evenly throughout the mold, it may be delivered from a charging device comprising a hopper with a discharge slot and means for admitting air to the hopper to carry the powder out through the slot. Another form of charging device which may be used is a hopper with a vibrating sieve. Such a sieve should have openings large enough to allow the powder to pass without severe vibration, as this would break some of the coarser aggregates. If B-nickel powder of bulk density 0.7 gram per cubic centimeter is used, a 150 to 170 Tyler or British Standard screen is suitable.

Unreinforced plates up to about 8 mm. thick can be produced with substantially no contraction parallel to the major surfaces by means of the invention. It is in these thin plates that the introduction of a grid causes substantial difficulties, so the invention is particularly valuable in enabling thin plates to be made without a grid. A grid can be incorporated in thicker plates without the same difiiculties but by itself does not adequately restrain contraction. By using rough or corrugated formers according to the invention and also incorporating a grid, plates thicker than 8 mm. can be made without any substantial contraction parallel to the major faces.

In carrying out the invention for continuous production, the novel apparatus comprises a charging device, a sintering furnace, and either a continuous mold or a series of molds mounted to move in a closed path beneath the charging device and through the furnace. In any case, the mold or molds present rough or corrugated surfaces onto which the powder falls from the hopper. Cover plates, likewise with rough or corrugated surfaces, are provided to fit individual molds or to cover the top of a continuous mold.

The apparatus comprises a series of rectangular molds 1 mounted to slide over a flat horizontal track 2 and each connected by an attachment 3 to an endless conveyor chain 4, the attachments 3 and chain 4 moving through a central channel 30 in the track 2. The conveyor 4 has horizontal upper and lower runs and passes over end wheels 5 and 6 as usual, the wheels 6 being positively driven from a shaft 7 at a low rate so that the molds move continuously but slowly. A charging device containing a hopper 8 is mounted above the top run of the conveyor and contains powder 27. One wall of this hopper is bent outwards as shown at 31 and within this wall there is a plate 32 which extends upwards as a rack 33 engaged by a pinion 34, so that the plate 32 can be raised and lowered. The base of the hopper is inclined as shown at 35, and a short wall 36 extends upwards in vertical alignment with the plate 32. A discharge slot 37 is left between the upper edge of the wall 36 and the lower edge of the plate 32 and can be adjusted in width by turning the pinion 34. A porous plate 38 extends across the hopper above the bottom 35 leaving an air space 39 into which air can be admitted under low pressure through a pipe 40. This air passes through the porous plate and carries powder out through the slot 37 in a uniform stream, which is deflected downwards by the part 31. This powder falls onto a refractory plate 28 made of unglazed ceramic material which fits closely inside the mold. To prevent powder falling through the small spaces left between successive molds, strips of a heat-resistant alloy 10 are provided, one on the front edge of each mold to project forwards into contact with the rear edge of the mold in front.

The molds, on leaving the charging device, pass beneath a V-shaped knife blade 11, the lower edge of which is slightly above the upper surface of each mold and by which the powder in the mold is substantially levelled and excess powder is removed. The molds then pass beneath a straight-edged knife blade 12 which is resiliently pressed into contact with the upper edges of each mold so that the surface of the powder is made completely level and flush with the edge of the mold. Powder pushed over or falling past the side edges of the molds falls into side channels 41. These channels also receive lugs 42 which project downwards from the sides of the molds 1 and serve to guide the molds. A hopper 25 leading to a storage bin 26 is provided to catch powder which may fall off the track 2 altogether or be pushed over the edges of the channels 41 when these are periodically cleared.

A stack of refractory cover plates 13 with rough surfaces is provided and a plate is put on the powder in each mold. The plates can be put in position automatieally by a device not shown. The mold, covered by a refractory plate 13, next enters a sintering furnace 14 through which the conveyor 4 passes. The conveyor and molds emerge from the furnace through insulation 15 into a cooling device 16 through which cooling water flows continuously. On arriving at the end Wheel 6 the cover plates 13 fall off the molds one by one and are caught by a rubber belt 17 having transverse ridges 18 spaced apart at such distances that a plate can fit easily between two successive ridges. This belt travels in contact with a stationary guide surface 19 over which the cover plates slide freely until the belt 17 is travelling substantially horizontally. At this point, the cover plates reach the end of the guide surface 19 and pass onto an endless conveyor 20 which carries them to the stack 13.

The sintered plates are held in the molds by a bank of electro-magnets 21 until they reach the beginning of the lower run of the conveyor. At this point, they pass out of the zone of influence of the electro-magnets and fall one by one into a receptacle 22. The molds are cleaned on the return lower run by brushes 23 and 24. The plates 28 are so tightly inserted in the molds that they do not fall out during the return run.

Other forms of apparatus may be used. For example, the apparatus may be circular with an annular mold made from a heat-resistant alloy with a rough or corrugated bottom. This mold may be slowly rotated about a vertical axis and in the course of its rotation pass through a sintering furnace and a cooling device. The cover plates in such a case are sector-shaped so that each extends over a part of the annular mold. As each cover plate emerges from the cooling device, it may be mechanically removed and deposited on the part of the mold about to enter tthe furnace. With such an apparatus, a continuous strip of sintered metal will be produced and this may be prized out of the mold in any convenient way and cut into lengths by a knife blade.

The present application is a division of my co-pending patent application Serial No. 83,164 filed March 24, 1949, and now abandoned.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be re sorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are con-- sidered to be within the purview and scope of the invention and appended claims.

I claim:

1. An apparatus for making porous magnetic metal plates by sintering magnetic metal powder between formers having opposed rough surfaces effective to prevent substantial contraction of said plates parallel to the major surfaces thereof, comprising in combination an endless flexible conveyor having a series of open-top molds, having a gravity-discharge end and having substantially horizontal upper and lower runs, each of said molds having a former comprising a rough-surface bottom portion of said mold interiorly thereof, said molds being connected to said conveyor for travel therewith in an endless path, charging means comprising .a hopper positioned above the upper run of said conveyor and adapted to dispense magnetic metal powder into each of said molds, levelling means positioned above said upper run and downstream from said'charging means with respect to the direction of travel of said upper run and adapted to remove excess powder from atop said molds, a magazine positioned above said upper run and downstream from said levelling means with respect to the direction of travel of said upper run and adapted to deliver a former comprising a cover plate having a rough surface onto the powder in each mold with the rough surface of the cover plate in contact with said powder, a sintering furnace through which said molds pass for sintering the magnetic metal powder in each mold to a porous magnetic metal plate, a cooling chamber through which said molds pass, said furnace and cooling chamber being positioned successively downstream from said magazine with respect to the direction of travel of said upper run, conveying means adapted tto receive the cover plates as they fall from said gravity-discharge end and to return them to said magazine exteriorly of said sintering furnace and cooling chamber, and magnetic means adjacent said gravity-discharge end and adapted to retain said porous magnetic metal plates in said molds until after said cover plates have fallen from said gravity-discharge end and adapted to release said porous magnetic metal plates subsequently for gravity discharge thereof from said molds.

2. An apparatus for making porous magnetic metal plates by sintering magnetic metal powder between formers having opposed rough surfaces effective to prevent substantial contraction of said plates parallel to the major surfaces thereof, comprising in combination an endless conveyor having a series of open-top molds, having a gravity-discharge end and having substantially horizontal upper and lower runs, each of said molds having a former comprising a rough-surface bottom portion of said mold interiorly thereof, said molds being connected to said conveyor for travel therewith in an endless path, charging means positioned adjacent the upper run of said conveyor and adapted to dispense magnetic metal powder into each of said molds, a magazine positioned adjacent said upper run and downstream from said charging means with respect to the direction of travel of said upper run and adapted to deliver a former comprising a cover plate having a rough surface onto the powder in each mold with the rough surface of the cover plate in contact with said powder, a sintering furnace through which said molds pass for sintering the magnetic metal powder in each mold to a porous magnetic metal plate, a cooling chamber through which said molds pass, said furnace and cooling chamber being positioned successively downstream from said magazine with respect to the direction of travel of said upper run, conveying means adapted to receive the cover plates as they fall from said gravity-discharge end and to return them to said magazine exteriorly of said sintering furnace and cooling chamber, and magnetic means adjacent said gravity-discharge end and adapted to retain said porous magnetic metal plates in said molds until after said cover plates have fallen from said gravitydischarge end and adapted to release said porous magnetic metal plates thereafter for gravity discharge from said molds.

3. An apparatus for making porous magnetic metal plates by sintering magnetic metal powder between formers having opposed rough surfaces effective to prevent substantial contraction of said plates parallel to the major surfaces thereof, comprising in combination a continuous conveyor having a substantially horizontal run and a discharge portion, and having a series of opentop molds, each mold having a former comprising a roughsurface bottom portion of said mold interiorly thereof,

said molds being associated with said conveyor for travel therewith in a continuous path, charging means positioned adjacent said run and adapted to dispense magnetic metal powder into each of said molds, a magazine positioned adjacent said run and downstream from said charging means with respect to the direction of travel of said molds along said run and adapted to deliver a former comprising a cover plate having a rough surface onto the powder in each mold with the rough surface of the cover plate in contact with said powder, a sintering furnace through which said molds pass for sintering the thus-covered magnetic metal powder in each mold to a porous magnetic metal plate, a cooling chamber through which said molds pass after passage through said sintering furnace, conveying means adapted to receive the cover plates as they are discharged from said discharge portion and to return them to said magazine exteriorly of said sintering furnace and cooling chamber, and magnetic means adjacent said discharge portion and adapted to retain said porous magnetic metal plates in said molds until after said metal plates have been discharged from said discharge portion and adapted to release said porous magnetic metal plates thereafter for gravity discharge from said molds.

4. An apparatus for making porous magnetic metal plates by sintering magnetic metal powder between formers having opposed rough surfaces effective to prevent substantial contraction of said plates parallel to the major surfaces thereof, comprising in combination first conveyor means having a discharge portion and having a series of open-top molds, each mold having a former comprising a rough-surface bottom portion of said mold interiorly thereof, said molds being associated with said conveyor means for travel therealong, charging means adapted to dispense magnetic metal powder into each of said molds, means adapted to deliver a former comprising a cover plate having a rough surface onto the powder in each mold with the rough surface of the cover plate in contact with said powder, a sintering furnace through which said molds pass for sintering the thus-covered magnetic metal powder in each mold to a porous magnetic metal plate, a cooling chamber through which said molds pass after passage through said sintering furnace, second conveying means adapted to receive the cover plates as they are discharged from said discharge portion and to return them to said cover plate delivering means exteriorly of said sintering furnace and cooling chamber, and magnetic means adjacent said discharge portion and adapted to retain said porous magnetic metal plates in said molds until after said metal plates have been discharged from said discharge portion and adapted to release said metal plates thereafter for gravity discharge from said molds.

5. An apparatus for making porous metal plates by sintering metal powder between formers having opposed rough surfaces effective to prevent substantial contraction of said plates parallel to the major surfaces thereof, comprising in combination conveyor means having a discharge portion and having a series of open-top molds, each mold having a former comprising a rough-surface bottom portion of said mold interiorly thereof, said molds being associated with said conveyor means for travel therealong, charging means adapted to dispense metal powder into each of said molds, means adapted to deliver a former comprising a cover plate having a rough surface onto the powder in each mold with the rough surface of the cover plate in contact with said powder, a sintering furnace through which said molds pass for sintering the thuscovered metal powder in each mold to a porous metal plate, and means adjacent said discharge portion adapted to separate said cover plates and porous metal plates and to return said cover plates to said cover plate delivering means exteriorly of said sintering furnace.

6. An apparatus for making porous metallic material by sintering metal powder between formers having opposed rough surfaces effective to prevent substantial contraction of said material parallel to the major surfaces 7' thereof, comprising in combination conveyor means adapted to carry metal powder in such a manner that a surface of said powder will remain exposed, said conveyor means having a discharge portion and including mold means having a rough surface contacting said powder, means adapted to deliver cover plates having a rough surface onto the powder carried by said conveyor means in such a manner that the cover plates substantially completely cover the exposed surface of said powder and the rough surface of each cover plate contacts said exposed surface, a sintering furnace through which said conveyor means passes for sintering the thus-covered powder carried by said conveyor means to porous metallic material,

8 and means adjacent said discharge portion adapted to separate said cover plates and material and to return said cover plates to said cover plate delivering means exteriorly of said sintering furnace.

References Cited in the file of this patent UNITED STATES PATENTS 2,074,185 Langhammer Mar. 16, 1937 2,350,179 Marvin May 30, 1944 2,368,458 Engle Jan. 30, 1945 2,554,343 Pall May 22, 1951 2,561,583 Marvin July 24, 1951 

1. AN APPARATUS FOR MAKING POROUS MAGNETIC METAL PLATES BY SINTERING MAGNETIC METAL POWDER BETWEEN FORMERS HAVING OPPOSED ROUGH SURFACES EFFECTIVE TO PREVENT SUBSTANTIAL CONTRACTION OF SAID PLATES PARALLED TO THE MAJOR SURFACES THEREOF, COMPRISING IN COMBINATION AN ENDLESS FLEXIBLE CONVEYOR HAVING A SERIES OF OPEN-TOP MOLDS, HAVING A GRAVITY-DISCHARGE END AND HAVING SUBSTANTIALLY HORIZONTAL UPPER AND LOWER RUNS, EACH OF SAID MOLDS HAVING A FORMER COMPRISING A ROUGH-SURFACE BOTTOM PORTION OF SAID MOLD INTERIORLY THEREOF, SAID MOLDS BEING CONNECTED TO SAID CONVEYOR FOR TRAVEL THEREWIGH IN AN ENDLESS PATH, CHARGING MEANS COMPRISING A HOPPER POSITIONED ABOVE THE UPPER RUN OF SAID CONVEYOR AND ADAPTED TO DISPENSE MAGNETIC METAL POWDER INTO EACH OF SAID MOLDS, LEVELLING MEANS POSITIONED ABOVE SAID UPPER RUN AND DOWNSTREAM FROM SAID CHARGING MEANS WITH RESPECT TO THE DIRECTION OF TRAVEL OF SAID UPPER RUN AND ADAPTED TO REMOVE EXCESS POWDER FROM ATOP SAID MOLDS, A MAGAZINE POSITIONED ABOVE SAID UPPER RUN AND DOWNSTREAM FROM SAID LEVELLING MEANS WITH RESPECT TO THE DIRECTION OF TRAVEL OF SAID UPPER RUN AND ADAPTED TO DEVLIVER A FORMER COMPRISING A COVER PLATE HAVING A ROUGH SURFACE ONTO THE POWDER IN EACH MOLD WITH THE ROUGH SURFACE OF THE COVER PLATE IN CONTACT WITH SAID POWDER, A SINTERING FURNACE THROUGH WHICH SAID MOLDS PASS FOR SINTERING THE MAGNETIC METAL POWDER IN EACH MOLD TO A POROUS MAGNETIC METAL PLATE, A COOLING CHAMBER THROUGH WHICH SAID MOLDS PASS, SAID FURNACE AND COOLING CHAMBER BEING POSITIONED SUCCESSIVELY DOWNSTREAM FROM SAID MAGAZINE WITH RESPECT TO THE DIRECTION OF TRAVEL OF SAID UPPER RUN, CONVEYING MEANS ADAPTED TO RECEIVE THE COVER PLATES AS THEY FALL FROM SAID GRAVITY-DISCHARGE END AND TO RETURN THEM TO SAID MAGAZINE EXTERIORLY OF SAID SINTERING FURNACE AND COOLING CHAMBER, AND MAGNETIC MEANS ADJACENT SAID GRAVITY-DISCHARGE END AND ADAPTED TO RETAIN SAID POROUS MAGNETIC METAL PLATES IN SAID MOLDS UNTIL AFTER SAID COVER PLATES HAVE FALLEN FROM SAID GRAVITY-DISCHARGE END AND ADAPTED TO RELEASE SAID POROUS MAGNETIC METAL PLATES SUBSEQUENTLY FOR GRAVITY DISCHARGE THEREOF FROM SAID MOLDS. 